1. Field of the Invention
The present invention relates to a liquid crystal display device comprising a transmission liquid crystal panel including a liquid crystal enclosed between a pair of transparent substrates and display pixels arranged in a matrix and a light source for irradiating an illuminating display light from a back of the transmission liquid crystal panel, and to a method of compensating for a luminance point defect of the transmission liquid crystal panel of the liquid crystal display device.
2. Description of the Prior Art
An example of this type of liquid crystal display device includes an active-matrix drive liquid crystal panel used for a projection device. This panel comprises a pair of glass substrates laminated to each other. One of the glass substrates has pixel electrodes arranged in a matrix on an inner surface thereof, and the pixel electrodes are connected to TFTS (thin film transistors). The pixel electrodes are selected by switching the TFTS, thereby displaying an image. In this construction, since no cross talk is generated as is generated in a simple matrix panel, a high quality display is realized.
The TFT has a multiple layer construction, in which a gate electrode, a source electrode, a drain electrode and the like are laminated on the glass substrate. The production procedure of the TFT is a repetition of the step of laminating such thin metal films on the glass substrate and the step of patterning the thin metal films by the use of a pattern mask. Accordingly, the production of a perfect TFT requires a great amount of effort to maintain and control various conditions in the production procedure.
It sometimes occurs that a defective TFT without normal TFT characteristics is produced. A defect which can be rectified is rectified in accordance with the type and the degree of the defect by the use of the appropriate rectifying technology. An example of a TFT defect is a luminance point defect, which is impossible to rectify on a circuit pattern and is recognized, for example, on a display screen in the form of a luminance point generated on pixels in correspondence with the pixel electrodes when the display screen is driven.
FIGS. 26 and 27 illustrate a conventional method of compensating for the luminance defect. An opaque shading film 206 is formed on a portion of a surface of a glass substrate 202, the portion being in correspondence with a luminance point pixel 205 of a liquid crystal panel 201. A light emitted from a light source (not shown) and incident on the luminance point pixel 205 is reduced by the opaque shading film 206, thereby making the luminance point pixel 205 inconspicuous.
Selected as the portion on which the opaque shading film 206 is formed, namely, a luminance point defect compensation area, is a portion through which the light from the light source is irradiated on the luminance point pixel 205. More practically, among irradiation paths of the light which is emitted from the light source, incident on the panel 201 through a condenser lens 207 and converged to a projecting lens 208, an irradiation path A passing through the luminance point pixel 205 passes through the compensation portion. FIG. 27 schematically shows that the luminance point pixel 205 and the opaque shading film 206 are on the same irradiation path. Among a pair of glass substrates 202 and 227, the glass substrate 202 is the one on which the light is incident. A liquid crystal as a display medium is enclosed between the glass substrates 202 and 227.
The opaque shading film 206 is formed in the following way: An ultraviolet-ray hardened resin ink is put on a fine curved surface at a tip of a marking needle and is transferred to the compensation area. Then, the ink is hardened by irradiating an ultraviolet ray, whereby the ink is adhered on the surface of the glass substrate 202. The opaque shading film 206 is extremely fine, although different in size depending on the type of the liquid crystal panel: the diameter is approximately 100 to 250 .mu.m and the thickness is approximately 10 .mu.m.
The above conventional method is limited in eliminating affects of the luminance point defect due to the following disadvantages:
(1) Since the opaque shading film 206 does not have an enough adhering force to the smooth glass substrate 202, the opaque shading film 206 is possibly peeled off from the glass substrate 202 or damaged when dust or the like is wiped off from the, glass substrate 202. Accordingly, it is poor in reliability.
(2) Since the opaque shading film 206 shutters the light almost perfectly, the opaque shading film 206 is recognized as a black point with the human eye when an image brightens the display screen. Accordingly, the compensation area is restricted within an end portion of the display screen.